Caracterização funcional da proteína salivar AS8.9KDA e avaliação de seu potencial como antígeno vacinal contra o carrapato Amblyomma sculptum (Acari: Ixodidae)

Abstract

Amblyomma sculptum is a tick belonging to the Ixodidae family, relevant to public health because it acts as the main vector of Rickettsia rickettsii, the etiological agent of Brazilian Spotted Fever. It also causes economic problems in livestock farming due to intense parasitism, reducing animal productivity and generating costs for control and treatment. The continuous and inappropriate use of synthetic acaricides has led to the emergence of resistant populations, posing risks to the environment and human health. In this context, anti-tick vaccines have been investigated as a sustainable alternative, and the salivary protein As8.9kDa was previously identified as a promising antigen in aluminum hydroxide assays. However, few studies have been conducted with this protein and its biological function for ticks is still unknown, as well as its vaccine potential when used in formulations with adjuvants other than aluminum hydroxide. Therefore, this study aimed to functionally characterize As8.9kDa and evaluate its vaccine potential against A. sculptum, using the adjuvants saponin, aluminium hydroxide and Montanide. Gene silencing of As8.9kDa resulted in a reduction of over 80% in mRNA expression in the salivary gland, as well as significantly lower recovery (56%) and hatching (35%) rates (p<0.05), indicating the protein's functional role in hematophagy. Among the adjuvants tested, aluminum hydroxide induced the greatest humoral response and was the only one that induced the greatest humoral response. Among the adjuvants tested, aluminum hydroxide induced the greatest humoral response and was the only one to show vaccine efficacy, but still less than 15%. A comparison between different brands of this adjuvant revealed that Aluminum Hydroxide Gel (Sigma) generated greater antigenicity than Alhydrogel® adjuvant (InvivoGen). These results emphasizethe importanceof As8.9kDa in tick biology and highlight the need to optimize vaccine formulations containing this antigen for the control of A. sculptum infestations.